(a) Technical Field
The present invention relates to a technique for calculating a Distance to Empty (DTE) in an electric vehicle. More particularly, the present invention relates to a method for more accurately calculating DTE in an electric vehicle, which enables a separate calculation of DTE reflecting a past accumulated fuel efficiency and DTE reflecting a current driving state and display both DTEs on a cluster.
(b) Background Art
Generally, electric vehicles are powered by one or more motors driven via electricity provided from a battery. In electric vehicles especially, it is essential to know and monitor instantaneous properties of a battery such as the temperature and the State of Charge (SOC). One of the reasons is that DTE based on a remaining capacity of a battery must be reported to a driver while driving by monitoring the SOC of the battery in real-time.
In internal combustion engine vehicles, a driver is informed of a DTE estimated based on the current fuel state. In electric vehicles, however, DTE (remaining travelable distance) is estimated from the current battery energy state, and then is shown on a cluster to the driver so that they can estimate how much further they can travel before they need to recharge the vehicle. As a typical method of calculating DTE of an electric vehicle, DTE is estimated using a relationship between a remaining energy of a high voltage battery and energy consumption rate per distance (i.e., the SOC %).
FIG. 1 is a flowchart illustrating a typical method of calculating DTE. Hereinafter, the typical method of calculating DTE will be described with reference to FIG. 1. The typical method of calculating DTE includes a process of calculating a past average fuel efficiency (S1), a process of calculating a current fuel efficiency (S2), a process of calculating a final fuel efficiency by blending the past average fuel efficiency and the current fuel efficiency (S3), and a process of calculating a DTE from the final fuel efficiency (S4).
Here, the past driving average fuel efficiency is calculated by averaging the fuel efficiency of past driving cycles (e.g., an interval from previous charge cycle to next charge cycle is defined as one driving cycle). The fuel efficiency (km/%) is calculated and stored at the finish of every driving cycle (e.g., the previous driving cycle is finished when charging has completed), and then the stored fuel efficiencies are averaged.
In this case, the fuel efficiency (km/%) of the driving cycle is expressed as an accumulation driving distance of driving cycle (km)/ΔSOC(%), where ΔSOC(%)=SOC(%) immediately after previous charge cycle−SOC(%) just before current charge cycle. Also, when the final fuel efficiency is calculated, DTE is calculated based on the fuel efficiency, and then displayed on a cluster, etc. In this case, DTE can be expressed as final fuel efficiency (km/%)×current SOC (%).
In calculating DTE of an electric vehicle, battery SOC is needed. Particularly, when the fuel efficiency of past driving cycles is calculated, the total battery consumption (corresponding to the above ΔSOC) during cycles is reflected. Particularly, energy consumption of past driving cycles needs to be reflected in calculating DTE, and in this case, the total battery consumption needs to be reflected. However, since the total battery consumption includes energy consumed by an air conditioning apparatus during the past driving cycles, it is difficult to calculate an accurate DTE which excludes the energy consumed by the air conditioning apparatus when it is not being used.
In order to overcome the above limitation, Korean Patent Application No. 10-2011-0135206, filed by the applicant of the present invention on Dec. 15, 2011 discloses a method for calculating DTE of an electric vehicle, which can accurately calculate DTE by removing energy consumed by an air conditioning apparatus to correct a past average fuel efficiency, and can more accurately calculate DTE by reflecting a fuel efficiency according to the operation of the air conditioning apparatus on the fuel efficiency calculated by blending the past average fuel efficiency and the current fuel efficiency to calculate a final efficiency. However, in all the existing DTE calculating methods, since DTE finally calculated is displayed on a cluster as a single numerical value, the fuel efficiency according to the current driving state cannot be accurately monitored.
In other words, as DTE reflecting both the past accumulated fuel efficiency and the current fuel efficiency according to the current driving state is displayed on a cluster as a single numerical value, fuel efficiency information about a current driving region of a certain distance cannot be accurately known during the operation of a vehicle.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.